The effect of transition metal (Mn, Fe and Co) doping to the Ce-site of the perovskite-type protonic conductor BaCe0.90Y0.10O3 - delta was examined. Single-phase samples of BaCe0.90-xY0.10MxO3 - delta were obtained at 0 <= x <= 0.10 for M=Mn and Co and at 0 <= x <= 0.075 for M=Fe. The conductivity of the samples in air decreased with transition-metal doping. Among the doped samples, Mn-doped solutions showed the lowest conductivity and the highest activation energy of conduction. The conductivity of these samples was independent of the concentration of the transition metals (x). This behavior of the conductivity could be explained by supposing the generation of the impurity state by transition-metal doping inside the band gap. In hydrogen, samples showed ionic conduction. The influence of transition-metal doping on the conduction behavior in hydrogen is small. (c) 2005 Elsevier B.V. All rights reserved.